A modern exhaust system includes an exhaust line which removes the exhaust from the internal combustion engine and is used to after-treat the exhaust gases, in particular to clean them. For example, an exhaust system in an exhaust line may include a particle filter which filters out the particles, preferably soot particles, that are entrained in the exhaust gas of the internal combustion engine, in particular a diesel engine, and incorporates them. Such a particle filter must be regenerated at certain intervals in time to prevent an excessive increase in backpressure in the flow through the particle filter. Such regeneration can be initiated by a short-term increase in temperature in the exhaust gas. The exhaust gas temperatures occurring in normal operation of an internal combustion engine are not sufficient for this, however. Accordingly, additional measures must be taken to raise the exhaust temperature accordingly. One possibility for raising the temperature in the exhaust is to introduce secondary fuel into the exhaust. This secondary fuel can then react with the residual oxygen contained in the lean exhaust, resulting in the desired increase in temperature. To support the oxidation of the secondary fuel, an oxidation catalyst may be arranged in the exhaust line upstream from the particle filter. It is likewise possible to design the particle filter itself to be catalytically active.
The situation is also similar for an NOx storage catalyst which may be arranged in the exhaust line in addition to or as an alternative to the particle filter to remove nitrogen oxides from the exhaust gases. An NOx storage catalyst must also be regenerated occasionally, to which end a reducing atmosphere is needed in the exhaust gas.
One problem with the introduction of secondary fuel into the exhaust is the fact that the secondary fuel must be present in vapor form to achieve the most complete possible oxidation. However, adequate vaporization of the secondary fuel injected into the exhaust line cannot be guaranteed at low exhaust temperatures.
The present invention is concerned with the problem of providing an improved embodiment or at least a different embodiment for an exhaust system of the type defined above such that the evaporation of the secondary fuel supplied to the exhaust in particular is improved even at low exhaust temperatures.